Salts of diaryliodonium compounds are used as polymerization initiators. For example, in patent documents 1-5, BF4, PF6, SbF6, AsF6 and other salts of diaryliodonium compounds having various side chains have been disclosed as polymerization initiators. These also include bis(dodecylphenyl)iodonium salts.
If the salts of diaryliodonium compounds are used as polymerization initiators, the phenyl moiety may be liberated by decomposition. As a result, for example, such compounds as benzene or toluene may be formed. These compounds have toxicity such as carcinogenicity, and thus their use has been restricted. In contrast to this, applicability of bis(dodecylphenyl)iodonium salts that are substituted with long chain alkyl groups such as dodecyl groups has been anticipated as polymerization initiators since the toxicity of dodecylbenzene produced by decomposition is relatively low.
However, although BF4 salts or the like of diaryliodonium compounds have been employed as polymerization initiators as mentioned above, there have been problems of poor compatibility of bis(dodecylphenyl)iodonium BF4 salts or the like with monomers. Although this problem is not serious at the small laboratory scale preparations of polymers, it may lead to problems of decrease in the efficiency of production at the industrial large-scale production.
Moreover, the BF4 salts or the like of diaryliodonium compounds are usually synthesized from diaryliodonium compounds and salts of halide ions. As halide salts, for example, chloride salts of bis(dodecylphenyl)iodonium have been disclosed in Patent documents 4 and 5. The said chloride salts have been synthesized by the dropwise addition of a mixture of sulfuric acid and acetic acid to dodecylbenzene and potassium iodate in a mixed solvent of acetic acid and acetic anhydride, followed by adding a solution of sodium chloride, cooling it to form a solid, and then recrystallizing the formed solid.
In Non-patent reference 1, examples of preparation of bromide salt and iodide salt of bis(dodecylphenyl)iodonium by a method similar to that of Patent documents 4 and 5 other than finally employing sodium bromide solution or potassium iodide solution have been reported.
Further, the conventional method of preparation of diaryliodonium compounds was not entirely satisfactory, and in particular, efficient method for preparation of diaryliodonium compounds substituted with long chain alkyl groups was not known.
For example, the methods for preparing bis(dodecylphenyl)iodonium salt disclosed in Patent documents 4 and 5 and Non-patent reference 1 deal with reacting potassium iodate (KIO3) and dodecylbenzene in the presence of acetic anhydride and concentrated sulfuric acid. However, this method has a low yield of 37-52%. This cannot be applied to the industrial mass production of diaryliodonium compounds. According to the findings of the present inventors, this method produces large amount of p-iodododecylbenzene as a byproduct. This p-iodododecylbenzene is difficult to separate from the target bis(dodecylphenyl)iodonium salt, and adversely affects the product quality.
Although as examples of preparation of diaryliodonium compounds having smaller substituents such as methyl groups or the like, the Non-patent references 2 and 3 contain example of reaction of sodium periodate (NaIO4) and aryl compounds in presence of concentrated sulfuric acid. Also, examples of preparation of di(4-isobutylphenyl)iodonium salt have been reported in Patent documents 6 through 9.
However, according to the findings of the present inventors, the yields are low when synthesizing diaryliodonium compounds in the absence of acetic anhydride. In other words, since even the yields reported in Non-patent references 2 and 3 are low, the prior art may not be applicable for production of diaryliodonium compounds substituted with long chain alkyl groups. The yields of di(4-isobutylphenyl)iodonium salt having been reported in Patent documents 6 through 9 are also low.
According to the findings of the present inventors, diaryliodonium compounds that are unsubstituted or substituted with lower alkyl groups can be prepared, for example, even by a method employing ammonium persulfate and employing iodobenzene and toluene as raw materials. On the other hand, diaryliodonium compounds substituted with long chain alkyl groups such as dodecyl group, for example, when made from the p-iodododecylbenzene and dodecylbenzene are used as raw materials, never proceed at all under the same conditions. Thus, in the preparation of diaryliodonium compounds, a large difference may be thought to exist in the reactivities of benzene or compounds substituted with lower alkyl groups and compounds having long chain alkyl groups. Therefore, examples of preparation of unsubstituted or lower alkyl substituted diaryliodonium compounds are not necessarily applicable for the preparation of long chain alkyl substituted diaryliodonium compounds.
Moreover, in Patent documents 6 through 9, while KIO3 has been used in the chemical equation, potassium periodate is mentioned in the text instead of potassium iodate. However, since in Patent documents 10 and 11, that refer to Patent documents 6 through 9 as prior art literature relating to the method of preparation of di(4-isobutylphenyl)iodonium salt, it is expressed as potassium iodate, it is thought that potassium iodate may have been wrongly mentioned as potassium periodate in Patent documents 6 through 9. In addition, the use of potassium iodate instead of potassium periodate may be a cause for low yields.
The following is a list of cited documents:    Patent document 1: Japanese Patent Application Publication 2005-120311    Patent document 2: Japanese Patent Application Publication Hei 7-3028 (1995-3028)    Patent document 3: Japanese Patent Application Publication 2001-11185    Patent document 4: Japanese Patent Application Publication Hei 6-184170 (1994-184170)    Patent document 5: Japanese Patent Application Publication Hei 6-41433 (1994-41433)    Patent document 6: Japanese Patent Publication Hei 7-55915 (1995-55915)    Patent document 7: Japanese Patent Publication Hei 7-57738 (1995-57738)    Patent document 8: Japanese Patent Publication Hei 7-64764 (1995-64764)    Patent document 9: Japanese Patent Publication Hei 7-116067 (1995-116067    Patent document 10: Japanese Patent Application Publication 1978-101331    Patent document 11: Japanese Patent Publication 1982-53767    Non-patent reference 1: F. Marshall Beringer and 6 others, Journal of American Chemical Society, vol. 81, pp. 342-351 (1959)    Non-patent reference 2: Lukasz Kraszkiewicz and another person, Synthesis, No. 15, pp 0.2373-2380 (2008)    Non-patent reference 3: Lukasz Kraszkiewicz and another person, Proceedings of ECSOC-9, International Electronic Conference on Synthetic Organic Chemistry, 9th., A022/1-A022/12 (2005)